California Code, Code of Civil Procedure - CCP § 876

(a) The pro rata share of each tortfeasor judgment debtor shall be determined by dividing the entire judgment equally among all of them.

(b) Where one or more persons are held liable solely for the tort of one of them or of another, as in the case of the liability of a master for the tort of his servant, they shall contribute a single pro rata share, as to which there may be indemnity between them.